1. Field of the Invention
The present invention relates to a low temperature-cured polymer gate insulation layer and an organic thin film transistor using the same, and more particularly, to a gate insulation layer with chemical resistance, heat resistance, and excellent surface characteristics that is capable of improving an electrical characteristic of an organic thin film transistor using a low temperature-cured polymer, and the organic thin film transistor using the same.
2. Discussion of Related Art
In general, a number of conjugated organic polymers display desirable physical properties that can possibily be exploited in various semiconductor configurations. A number of organic semiconductors materials has been actively studied in hopes of exploiting their respective physical properties in new electric and electronic materials. It is hoped that these unique physical properties exhibited by conjugated organic polymers may be able to be exploited in a number of broad fields such as functional electronic devices and optical devices. Some of these unique physical properties include a wide diversity of synthesizing methods, easiness in shaping a fiber or film form, flexibility, conductivity, and a low production cost. Many of these unique physical properties could not be obtained from conventional inorganic semicondutors such as amorphous silicon or poly silicon.
Among these devices include the well known organic thin film transistor which use organic materials as an active region. The organic thin film transistor is almost similar in structure with a the silicon thin film transistor (Si-TFT) except that the organic material is used instead of silicon (Si) in a semiconductor region. In the organic thin film transistor, a thin film can be more conveniently formed by using room-pressure wet method methods (printing coating, spin coating, and bar coating), instead of using chemical vapor deposition methods that require plasma for forming a conventional silicon thin film. Further organic thin film transistors enioy the advantage in that a relatively low-priced transistor can be realized using a roll to roll manufacturing technique that uses a plastic substrate.
At present, it is expected that the organic thin film transistor be used for a driving device of a plastic-based active type organic light emitting device, a smart card, and an inventory tag plastic chip. The efficiency of the organic thin film transistor is dependent on crystallization of an organic active layer, a charge characteristic of an interface between an organic insulation layer and the organic active layer, a thin film characteristic of the organic insulation layer, and an ability for carrier injection into an interface between a source/drain electrode and the organic active layer. In order to improve such the characteristics, various methods are being attempted.
A material is required to have a low electrical conductivity and a high breakdown field characteristic in order to be used for a gate insulation layer of the organic thin film transistor. While a silicon oxide layer is presently used as the gate insulation layer of the organic thin film transistor, a ferroelectric insulator series such as BaxSr1-x TiO3 (BST), Ta2O5, Y2O3, and TiO2 and an inorganic dielectric substance having a larger permittivity, such as PbZrxTi1-xO3 (PZT), Bi4Ti3O12, BaMgF4, SrBi2(Ta1-xNbx)2O9, Ba(Zr1-xTix)O3 (BZT), BaTiO3, SrTiO3, and Bi4Ti3O12, are used to reduce a threshold voltage (U.S. Pat. No. 5,946,551, and Korean Patent Laid-Open Publication Nos. 1020020084427 and 1020020034873).
A film-forming temperature of an inorganic insulation layer is high and therefore, when being applied to the organic thin film transistor, it can have influence upon physical/chemical properties of a substrate used (particularly, a plastic substrate) and other layers formed on the substrate in an earlier process (Hereinafter, referred to as “earlier processed layer”), thereby affecting a transistor characteristic. Accordingly, a low temperature process is made possible so that a research on a new organic gate insulation layer capable of minimally affecting the earlier processed layer is under active progress. An example of the organic insulation layer includes polyimide (Korean Patent Laid-Open Publication No. 1020030016981), poly vinyl alcohol (Korean Paten Laid-Open Publication No. 1020020084427), poly (vinyl phenol-maleiimide) (Korean Paten Laid-Open Publication No. 1020040028010), and photo acryl. However, they do not have a device characteristic to substitute for the conventional inorganic insulation layer. Accordingly, in order to implement a high-efficiency organic thin film transistor, it is highly required not only to develop a material for the organic active layer but also to develop a polymer gate insulation layer with an excellent device characteristic in which the thin film can be formed through a simplified process without affecting the substrate and the earlier processed layer.
Accordingly, inventors of this application discovered that, when the gate insulation layer is formed of an acrylate-based compound, an anhydride-based compound, and an epoxy-based compound, it can be cured at a low temperature, and the formed gate insulation layer has excellent chemical resistance, heat resistance, and surface characteristics and further, discovered that applying the formed gate insulation layer to organic thin film transistors improves an electrical characteristic, and completed the present invention.